From DE 198 58 541 A1 and DE 198 58 543 A1 electro-hydraulic transmission control devices for six-gear automatic transmissions with five shift elements are known, in which shift elements are engaged in the force flow of a drivetrain of a vehicle both to produce transmission gears for forward driving and to produce at least one reverse gear.
A disadvantage here, however, is that in the event of a wrong command in the transmission at any time, even without a corresponding driver's wish indication, a change from a gear for forward driving to the at least one gear for reverse drive can take place, where unsafe driving situations can be created and unacceptably large loads in the drivetrain of a vehicle can result in component damage.
To prevent an undesired gear change in a transmission, pressure sensors or valve displacement sensors, are provided such that a wrong command from a transmission control device can be recognized before a gear change. Thus, the transmission is constructed with a fail-safe, but this is elaborate and cost-intensive.
In addition, in the transmission control devices known from the prior art, two of the shift elements are alternatively controlled by a common pressure control valve. As a result of the connections between the pressure control valve and the shift elements, it's controls are respectively temporarily cut off during the alternating control, and air collects in the connection lines between the pressure control valve and the shift elements controlled by it. In practice, these air accumulations can only be removed by elaborate means or prevented by appropriate hydraulic measures which entail high costs. Furthermore, the change between the two procedures can only be effected by actuating a correspondingly modified electro-hydraulic transmission control device in a very elaborate manner.
Accordingly, the purpose of the present invention is to provide a transmission control device such that both an undesired shift in the transmission between gears for forward driving and a reverse drive gear and air accumulations can be reliably prevented inexpensively and with little control and regulation effort.